1. Field of the Invention
The present invention relates to a method for estimating a plane in a captured range image and to a range image camera, and more particularly to a method for estimating a plane in a captured range image by precisely measuring per pixel the time taken for projected light to be reflected back by a target, and to a range image camera to which such a plane estimation method is applied.
2. Related Art
Heretofore, various techniques that involve using a captured image of a target space to perform processing such as monitoring the target space and extracting the appearance of a target object in the target space have been proposed. However, there is a problem in that because the image used in such techniques is a gray scale image that reflects the tones of the target space and is thus affected by changes in the amount of external light, these techniques can only be used in an environment in which there is very little change in the amount of light.
In view of this, techniques have also been proposed that enable a target object to be extracted without being affected by changes in the amount of light, by employing a configuration for generating a range image having ranges for pixel values, and extracting the target object using the range image.
However, with such a range image, the range values may be unstable with only the data of single pixels, making it difficult to clearly separate between a human body serving as the target object to be extracted and a floor surface. Thus, at present, the foot of a human body is separated from a floor surface using devices such as increasing the angle of elevation, so as to intentionally not include the contact area between the foot of the human body and the floor surface in the viewing angle, for example.
As for image processing apparatuses using range images, techniques have been proposed that, for example, enable a target object to be separated even in the case of a small range difference between the target object and the background, by generating a difference image from a plurality of range images obtained at different times (e.g., see JP 2006-053791A).
However, these techniques simply separate the background, and do not actively recognize planes in a range image.
As for methods for searching for planes in a captured image, techniques such as “Plane Estimation Method using Stereo Images and Object Detection Apparatus” (JP 2004-094707(a), hereinafter “Patent Document 2”), “Autonomous Mobile Apparatus and Planar Obstacle Recognition Method” (JP 2007-121258A, hereinafter “Patent Document 3”), and “Robot Apparatus, Stair Climbing Method therefore, and Mobile Apparatus” (WO2005/087452A, hereinafter “Patent Document 4”) have also been proposed.
Of these, the technique disclosed in Patent Document 2, although enabling a plane to be estimated with a high degree of accuracy even when an object other than a plane exists in an imaging area, is limited to use with stereo images. The main object of the technique disclosed in Patent Document 3 is to accurately recognize the position of a planar obstacle serving as an obstacle, particularly the position of a planar obstacle having a void. The technique disclosed in Patent Document 4 is configured such that recognition of a step having a movable plane and judgment as to whether the step can be climbed are performed, so as to enable the mobile object to perform an autonomous climbing operation itself after acquiring information relating to the step.
In order to animate a human body model freely in a range image with a small amount of computation, it is necessary to clearly separate the floor surface and the foot with small amount of computation. However, the abovementioned conventional techniques are not necessarily suitable for realizing this.